300E 300E Belt Tensioner: how to test shock absorber?

[azurite300E]

Today I went into the belt tensioner to fix a non-working adjustment rod. Last time the belt was replaced, I adjusted the tension and it seemed ok. Then a few days later once the belt had settled I needed to readjust the tension, but even after loosening the 19mm bolt, the treads of the adjusting rod stripped. Just took everything out and managed to repair the treads on the rod with a fine file and now the rod is once again tensioning the belt properly.

While I was in there, I noticed that the lower end of the shock absorber (the end that goes towards the tensioning device) was hanging loose. The shock absorber was just being supported at its upper end. On the lower side both the nut and bolt on the lower side are gone, the bushing on the absorber mount was also gone. Don't know what happened there, because I'm certain I reinstalled it correctly when I replaced the belt some time ago. Do these come loose over time just like that? BTW, I looked on the protective tray bellow the engine, but none of the missing parts where there. Would have found them on my last oil change anyway.

I wanted to know what would be correct procedure to test this shock absorber, as mine seems to have only fair resistance when I try to pull it apart, but a lot of resistance is felt when pushing it together. Feels like about 10:1 ratio of resistance. Is this normal, strong resistance only one way, and only fair resistance the other way? This is an OEM MB part, number 103-200-0114.

Would like to make sure this shock is still ok before I embark in trying to find a replacement for the missing bushing on its mount in order to reinstall it. The nut and bolt I've to get anyhow, but not sure how easy it will be to locally find a bushing that will fit.

Thanks in advance for any information.

[azurite300E]

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[S-Class Guru]

Your shock seems okay from your description. It should be very stiff one way, and quite easy the other way. Just hold it upright in the normal vertical position and pull/push it. If it moves smoothly with no roughness or "bumps and skips" then it's fine.
However, that's a moot point, cause you very likely cannot find a rubber bushing to go in it. These are pressed into the eyelet. The normal fail mode for these (other than coming unbolted) is hardening/shrinking of the bushing, which makes them click when the engine runs. If you find one, and find a way to install it, please let me know; I have a couple of good shocks with clicking bushings.

Oh, with the shock loose, you may have trashed your tensioner - it's just a big rubber bushing itself, and would see a lot of additional abuse without the shock to dampen it's rotation. If you had to readjust it, it's probably going.
If it fails, you get towed home.

DG

[azurite300E]

Hi DG,

Thanks for the input. According to your description my shock should be just fine, it performs very smoothly, no bumps or any roughness can be felt along the whole travel. What actually fell out (along with the nut bolt and nut) is the metal bushing, as the eyelet still has the rubber ring where the bushing used to be seated. This week I will take a trip down to the local hardware store and figure out what to use instead of the bushing and that will fit snugly inside the rubber ring, so it wont click while in operation.

Fortunately my tensioner is still working perfectly, I tested it when I took it out this past Sunday, and so far the belt is holding nicely tight. It probably survived because the belt wasn't very tight to begin with, so it was actually the belt that was taking whatever abuse. I closely inspected the belt too, and found no sign of any damage either. I've been driving the car for over three years /about 5000 miles (wow time flies!) since I replaced the belt (and water pump), but like I posted earlier, I was never able to fully tighten it up. I only heard an occasional short screech when hard shifting from 1st to 2nd gear, that certainly reminded me every time that I still had to deal with this problem sometime.